Road studs are in widespread use to provide visible guidance and warnings to motorists and other road users. Such road studs typically include one or more reflectors made out of glass or plastic to reflect light from vehicle headlights. The road studs help a motorist to determine his or her position on the road during hours of darkness.
There are two main types of road stud in use in the UK. The first is generally known as a “stick on”, and is normally formed from a plastic unit incorporating one or more plastic reflectors. Plastic stick-on reflectors are placed on top of the surface of the road and are attached to the road by adhesive. They are relatively cheap but also have a relatively short life-time. For example, they may become detached from the road surface by passing traffic, and/or the visibility of the reflector may become reduced, for example by dirt being deposited onto the surface of the reflector.
The other main type of road stud in use in the UK is a depressible (also sometimes referred to as a “cat's eye”). This comprises a base unit, normally made of cast iron, which holds a resilient insert. The insert is typically made of rubber, and carries one or more glass or plastic reflectors. This type of road stud is installed by drilling a hole in the road, and then bonding the road stud into location using bitumen or some other road grout.
The inserts for depressible road studs are generally provided with one or more wiper blades. When the insert is compressed, for example because a lorry has driven over the road stud, these blades are designed to wipe across the reflectors. This helps to keep the surface of the reflectors free from dirt, and hence helps to maintain high visibility.
One example of a depressible road stud is described in GB 2263298 B. A road stud generally in accordance with this patent is sold commercially under the “Light Dome” trademark by Industrial Rubber plc, of Fareham, Hampshire. The insert described in this patent includes ducts to allow water that has collected in the base of the road stud to be applied to the wiper blades. The water helps to lubricate the wiping action of the blades on the reflectors, thereby reducing wear, as well as assisting with the overall cleaning process.
It is also known to make a hybrid road stud, which involves a plastic reflector stuck on to a cast iron base unit that is sunk into the road. This road stud is designed to ensure greater permanence for the reflector (compared to adhering the plastic reflector directly onto the road surface), but does not have the wiping action of a depressible to keep the reflector clean. The use of this hybrid road stud has been rather limited in practice.
The typical weight of a conventional base unit made of cast iron is approximately 5 kg. Although the large weight of the base unit assists in retaining the stud in the road, it does mean that the base units are relatively expensive to transport around the country since they are so heavy. In addition, it is difficult to machine lay such heavy road studs. Rather, the road studs are generally laid by manual workers by hand. However, the weight of the stud may cause some safety concerns, for example a base unit might cause injury if dropped onto the foot of a worker.
It has been contemplated for many years that the base unit of a depressible road stud could be made of plastic rather than of metal. For example, GB 2280922 A suggests a base unit formed of a plastic material such as nylon. The use of a plastic base is also suggested in GB 2121463 A and GB 2229470 A. Nevertheless, no-one has yet managed to bring a successful plastic base unit for a depressible road stud to the market, and all depressible road studs in use in the UK still have metal base units.